Manufacture of insulating material



Jan. 23, 1934. KRONSTEIN 1,944,562

MANUFACTURE OF INSULATING MATERIAL Filed. March 13, .1928

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i a $125M W724i (Z Z aZ/a/we Patented Jan. 23, 1934 PATENT; oFncE MANUFACTURE or iusumrmo MATERIAL Abraham Kronstein, Karlsmhe, Germany, as-

signor to the firm Electra-Lackwerke G. m.-b.' H. System Dr. Kronstein, Karlsruhe, Germany Application March 13, 1928, Serial No. 281,417, and in Germany July 2, 1927 7 Claims. (01. 154-23) This invention refers broadly to electrically insulating material, and it is intended among other important objects to devise means of improving the quality and the life of such products,

to increase their resistibility both against electric influences as well as against the action of moisture and heat and atmospheric agents, and to generally improve and facilitate the process of manufacture. In the electric arts it has been 10 common to mainly employ rubber and the socalled linoxyn, that is to say the oxidation product obtained by the action of air upon linseed oil, preferably heated linseed oil, and oil varnish, as insulating materials, besides other substances, all such insulating compounds being usually combined with other insulating agents; such as paper, linen, silk and equivalent means, all of which possess a higherdegree of mechanical strength and resistibility. The manufacture of these products has been mostly carried out by applying a solution of the rubber or of the linoxyn unto the material of higher mechanical resistibility, and by then drying the coating obtained. This drying procedure must be carried out by oven--or furnace-heat or by means of hot air, in order to completely remove the solvent, and to produce a dry and solid layer. In the case of the linoxyn, insulating oil-varnish has been usually employed as the starting material for the manufacture, the procedure being such that the linoxyn has been generated only in contact with the carrier base, such as silk, linen, paper and the like. With this manner of operation the nature of the fibre of the carrier is very injuriously affected by the heat employed, so that the strength and permanency of the material are considerably reduced. After a certain time various defects are presenting themselves which are generally designated as collapsing phenomena, and the insulating material as a result thereof becomes brittle, and the insulating qualities are decreased with the additional drawback that the material is gradually losing its resistibility against the entrance of moisture.

- Now, these difficulties are overcome in accordance with this invention by combining an electrically insulating material, such as for instance rubber-solution, solutions of artificial resins, insulating varnish, thatis to say, so-called oil- '50 varnishes, including the linoxyn, or so-called zapon"-varnishes, that is to say, celluloid-varnishes, solutions of nitro-cellulose with or without camphor, or solutions of celluloid in acetone, amyl-acetate, ether or the like,- including solutions of'acetyl-cellulose or of nitrocellulose genjectionable on account of their becoming decomposed by friction and by the influences of the electric currents and electro-magnetic fields which cause them to liberate their acid constituent and to swell up and assume a porous condition. It should also be noted that the cellulose-compounds containing nitrated constituents are inflammable by shcrt-circuiting. Then, in the employment of these and similar carriers for electric insulating and allied purposes it is of paramount importance to avoid the presence of fibers in the insulating units, inasmuch as impregnated fibers are'subject to ageing and become brittle, and even the slightest amount of projecting'fibers is liable to produce sparking. The suggestions contained in the previous art, so far as Ipam aware, have failed to produce insulating units from cellulose-material which are both heat-proof as well as nonswelling andfree from fibers. In view thereof I have entirely discarded the use of cellulose- 85 esters and instead thereof my invention provides for the use of substantially pure homogeneous and not esterfied cellulose as obtained by the solidification of more or less dissolved cellulose. Such kinds of cellulose are for instance designated by various fancy names, such as Cellophan, Transparit", GaudophiP and others, all these substances or compounds being obtained from cellulose by treatmentwith carbon-disulfid and soda-liquor or caustic soda and containing a certain'amount of glycerine which makes them transparent or translucent. The cellulose-product by itself is a very 'poor insulator. Now; I have found in the course of my experiments that by the combination of a carrier base orlayers of these cellulose-products with the .electrically insulating agents above enum'erated it is possible to produce a material, which is free from fibres and possesses an exceedingly high degree of electric' resistance, and which will retain its valuable properties for an unlimited lengthi of time, and which, moreover, is water-proof and is not affected by high temperatures, so as to be particularly well adapted for use in the electricvarts for various purposes.

In view of the fact that'the product resulting from the combination 'of materials referred to presents a new composition, free from fibers,

which is not affected by high temperatures, it becomes possible to combine the cellulose-products with the varnish at high temperatures, without thereby in anyway detracting from the flexibility or resistibility of the final product.

While the electrically insulating materials heretofore known and comprising a combination of fibrous material and varnish constitute a film or a membrane of linoxyn through'which gases will diffuse, so that they are not adapted to produce a suificient protection oi electric machines against moisture and acid vapors, the product according to my invention is absolutely impermeable for gases and water. The product obtained in the manner described is moreover oil-proof, and the costs of manufacture thereof are nevertheless lower'than those of compositions in accordance with the previous methods. This is rnainly due to the fact that the cellulose products above referred to, asfound in commerce, produce smooth-faced carriers,,while in the case of other carriers, such as linen, silk, paper-or the like, rather expensive operations were necessitated, in order to cause them to present a smooth outer surface, it being well known that smoothness of surface of the insulating material is an indispensable requirement for'the prevention of electric discharges.

The process of manufacture of the insulating material may be carried on in different ways. Thus I may proceed for .instance by applying the insulating compound, such as linoxyn, rubber or a rubber-mixture or--comp ound to one side of the cellulose material, by which means an insulating material or an insulating band or ribbon having any desired degree of adhesiveness and possessing a smooth,- hard back surface of cellulose material is obtained which is particularly adapted for use with low voltages. However, it is also possible to coat this material on the other untreated side with the same material or with an insulating material of other qualities, so that a new product is obtained the properties of which may be varied in any suitable manner as compared with the materialcoated on one side only. Thus it is possible in'this manner to impart a higher insulating action to one side of the material than to the other side thereof.

By using 'coats. of-diflerent thickness on both sides of the carrier bending of the electric insulating units thus obtained isfacilitated. the elasticity is vastly increased and all tendencies of cracking of the coating are eliminated. Any

desired changes or varieties asregards mechanical properties, resistance, self-induction .or capacity of the two coats and'as regards other qualities may be produced; or an insulating band or ribbon may be obtained according to this invention which is provided on one side with an adhesive agent, while the other side thereof is highly insulating and accordingly dry and free from adhesive properties. Y

In the case of insulation being provided on,

both sidesof the article the insulating layers may be of the same or of ,diiferent thicknesses on 'both'side's I 0 {j The cellulose-composition according to this inj; ,vent'ion' is freefrom fibres. and free-from ester. constituents and accordingly not liable to lose itsimpermeability by decomposition it may employed moreover; forthe manufacture "oi finished articles, suchas electrically insulating lose-material which has been varnish-coated on one side or on both sides by the pasting together of two or a plurality of such insulating layers or by producing a combination or aggregation thereof in any other suitable manner. These articles will then comprise a large number of superimposed insulating layers by which means the electric resistance becomes exceedingly high. It is also possible, of course, to obtain finished articles from cellulose-compounds free from fibres which possess the final shape of the desired insulating unit, and then convert them into the superior insulating composition and articles by the applicationof insulating compounds, such as linoxyn or oil-insulating varnish or the like, after having imparted the final shape to such bodies. I The invention is illustrated diagrammatically and by way of example on the accompanying drawing in Figures 1 to i-showing longitudinal sections through pieces of insulating units according to my invention, the cellulose base or a carrier being designated a in all of the figures, while b and c are layers of insulating material,

linoxyn or the like, as above set forth and respectively disposed on the two sides of the carrier a. In Figure 3 a comparatively thinner layer d of a suitable adhesive is arranged at the bottom side of the carrier bases. In Figure 4, I have shown diagrammatically an aggregate of superimposed pairs of layers a of cellulose with interposed layers of insulating material b.

It will be obvious and should be understood that variations and modifications are possible as regards the manner of combination of the constituents of the insulating products and articles described, and it is therefore aimed to cover all modifications and embodiments of the principles .of the invention, which do not involve a deparsaponifiable carrying sheets of viscose-like, solid 3 regenerated cellulose and a coating of solidified linseed-oil oxidation products.

2. As new articles of manufacture electrically insulating units, comprising impermeable. wa-

ter-prooi, thin and flberless, unsaponiflable carry'ing sheets of viscose-like, solid regenerated cellulose and a coating of homogenous, rubber: like and stretchable, substantially oil-proof, water-insoluble, organic solid electric insulating material, superficially and firmly united to saidl it carrying sheets.

3. As new articles of manufacture electrically insulating units, comprising impermeable, water-' proof, .thin and fiberiess'fsub'stantiallyt anspar- 1 ent, unsaponiflablecarrying sheetsiof like, solid regenerated cellulose and a. homogenous coating-of solidified linseed-oil onid'ation products superficially and firmly adhering tosaid base.

4. As new articles of manufacture electrically insulating units comprising a thin and fiberless sheet of impermeable, water-proof, solid, viscoselike regenerated cellulose, a comparatively thin coating 'of solidified linseed-oil oxidation products on one side of said sheet, and a comparatively thick coating of such linseed-oil products on the opposite side of the sheet, said coatings being superficially firmly united to said sheet.

5. As new articles of manufacture electrically insulating units, comprising a thin and fiberless sheet oi impermeable, water-proof, solid viscoselike regenerated cellulose, a coating of sdlidified linseed-oil oxidation products on one side of said sheet and superficially firmly united thereto, and an adhesive coating on the opposite side of said sheet.

6. As new article's oi manuiacture insulating units, comprising a thin and fiberless sheet of impermeable, water-proof regenerated glycerinecontaining cellulose and a coating of homogenous, rubber-like and stretchable, substantially oil-proof and water-insoluble, organic solid, electric insulating material superficially firmly united to said sheet.

7.'The method of manufacturing electrically insulating units which comprises coating sheets of solid, viscose-like and fiberless regenerated cellulose at ordinary temperature with linseed-oil oxidation products and causing said products to become firmly united and solidified in permanent contact with the surface of said sheets.

ABRAHAM KRONSTEIN. 

